1. Field of the Invention
The present invention relates generally to molded tables. More particularly, the present invention relates to a molded plastic table structure having multiple concurrently molded layers.
2. Related Art
There are a variety of folding tables, including folding tables with plastic tabletops, such as are used in hotels, banquet halls, public buildings, churches, temporary household use, etc. Typical folding tables have folding legs that fold against the underside of the table, to enable easy moving and storage, while minimizing the storage space required.
The tops of prior art folding tables are usually fabricated of particleboard or laminated plywood, and may include a hard surface facing on the top. These tables typically incorporate a steel frame and folding steel legs. Unfortunately, these tables present a number of common drawbacks. The edges of metal frame members can be sharp and injure the fingers of people handling the tables. Particleboard and plywood tops tend to break easily if dropped, and are susceptible to moisture, which, if absorbed, may damage the tabletop, or discolor the surface. These tops also tend to bend and flex excessively when too much weight is placed on the table, and attempts to strengthen them tend to merely add to bulkiness and weight.
To overcome some of these problems, folding tables with an aluminum tabletop have also been fabricated. Unfortunately, these tables are relatively expensive, and are also susceptible to undesirable wear and tear, producing dents and sharp edges.
Plastic materials have recently come into use for the fabrication of lightweight folding tables, including plastic tables with lightweight cores, having plastic layers or grid frameworks as reinforcing members with plastic layers in various forms. Prior plastic tables are typically fabricated by forming a skin, such as by blow molding, rotational molding, injection molding, or vacuum forming. This tends to create a weak shell. A frame may be disposed within the shell or connected to the exterior of the shell to add structural rigidity, and a plastic foam material, such as polyurethane foam, may also be injected into the shell to increase the stiffness of the tabletop. This method produces a relatively good finished plastic table structure.
Unfortunately, the number of steps and secondary processes required to form such a table are costly and time-consuming for the producer. For example, injected foams produce relatively high fluid pressures (e.g. 40-50 psi), thus requiring a very strong support structure, fixture, or mold to contain the hollow skin when the foam core is injected and expands. Consequently, injected foams are typically applied in a step separate from the table molding step because thick heavy molds capable of withstanding the post-foaming pressures are too heavy and bulky for the rotational or blow molding processes. Such molds would also be thermally inefficient, and would impose impractically large loads on molding equipment. Additionally, because the foam core is formed through injection, there is a substantial likelihood of delamination of the skin from the foam core. Finally, injected polyurethane foams are relatively expensive.